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Author Topic: Right propellor versus speed ??  (Read 3119 times)

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Dutchman

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Right propellor versus speed ??
« on: August 27, 2010, 04:05:41 AM »

Dear Catalina owners,
We have a C34MK2, with an Universal 35BC.
My experience:
1800 rmp/min : 5.9 knots (my cruising speed for long distance).....fuel 2.5 ltr/hr
1900 rpm/min: 6.0-6.1 knots
2100 rpm/min: 6.5 knots
2300 rpm = the maximum speed 7.1 knots and is  little below the hull speed ? The swimmingplatform surface is just in the water.

So my opnion.....do I have the right propellor/pitch ??

Please give me your information and experience with your boat.

Best regards,
Ton Eijsermans
Amuse

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Ken Juul

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Re: Right propellor versus speed ??
« Reply #1 on: August 27, 2010, 04:52:06 AM »

The first step in this process is to ensure that the tachometer is reading correctly.  You can purchase a laser rpm gun or your local boat mechanic should have one.  There are instructions in the tech wiki for adjusting the tach.

The speed profile you presented looks about right, you are not going to get much more than about 7 knots.  If the tachometer is determined to be correct, then I would say you are over pitched, the engine should reach close to 3000 rpm under load.
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Ken & Vicki Juul
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Joe Kern

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Re: Right propellor versus speed ??
« Reply #2 on: August 27, 2010, 06:26:08 AM »

I agree with Ken.   The RPMs seem low across the entire range to me.   Even with a clean bottom and clean prop 7 knots at 2300 rpm is much different than my experience.
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Joe Kern
2005 Catalina 34MKII
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Stu Jackson

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Re: Right propellor versus speed ??
« Reply #3 on: August 27, 2010, 07:28:15 AM »

Uhmm, maybe I missed it, but what pitch do you have on your prop?  What prop do you have?  Otherwise, we're all in the dark on this one.
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Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

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Ron Hill

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Re: Right propellor versus speed ??
« Reply #4 on: August 27, 2010, 06:41:16 PM »

Tom : Look at my Mainsheet Article a few issues back on "RPM & Boat Speed."  I also talk about prop pitch.  A thought!!
« Last Edit: August 28, 2010, 06:36:59 PM by Ron Hill »
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Ron, Apache #788

Tom Clay

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Re: Right propellor versus speed ??
« Reply #5 on: August 29, 2010, 04:04:29 PM »

Ton,

We also own a MK11. We have the standard 3 blade prop supplied by Catalina. Your numbers are exactly what we see on our boat, even the swim platform item is the same. We do occasionally cruise at 2500 RPMs which give's us a hull speed of 7.3 knots.The majority of our time is spent at 2300-2400 rpm at 7.1-7.2 knots and we gain very little beyond 2600 RPM. Folks that cruise together with us are very surprised at how well she cruises.

1800 rmp/min : 5.9 knots (my cruising speed for long distance).....fuel 2.5 ltr/hr
1900 rpm/min: 6.0-6.1 knots
2100 rpm/min: 6.5 knots
2300 rpm = the maximum speed 7.1 knots and is  little below the hull speed ? The swimmingplatform surface is just in the water.
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Tom and Lynn Clay
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SeaFever

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Re: Right propellor versus speed ??
« Reply #6 on: August 29, 2010, 07:04:47 PM »

One question I would have is whether you are able to achieve your engine's rated max RPM or close to it. If not, you are perhaps over-pitched already. If you are, then you proceed at looking at other parameters...I have a M25 and don't remember the rated max rpm for the 35.
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Mahendra, Sea Fever, Pearson 10M, #43, Oakland, CA

Ron Hill

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Re: Right propellor versus speed ??
« Reply #7 on: August 31, 2010, 06:00:59 PM »

Guys : The entire thrust of my Mainsheet article is : The rpm that you are quoting it it the Tach gage numbers ? or the real engine RPM numbers?( from a laser tach gage) 
It sure makes a difference!!   :shock:
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Ron, Apache #788

horsemel

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Re: Right propellor versus speed ??
« Reply #8 on: August 31, 2010, 06:30:33 PM »

Ron,
Is a laser tach gage expensive?  I assume you can get them at an auto parts store.  Do tool rental places rent them?
Mark Mueller
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Craig Illman

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Re: Right propellor versus speed ??
« Reply #9 on: August 31, 2010, 07:36:40 PM »

Mark - I think about $35, for sure less than $50.

Craig
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prh77

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Re: Right propellor versus speed ??
« Reply #10 on: September 01, 2010, 05:41:08 AM »

I picked up a new one on Ebay for $22. Put the reflective tape on the pulley and found my tach was reading 300 RPM low. That explained a lot of things...
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Peyton Harrison Hull # 597 1988 "Trinity"

Ron Hill

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Re: Right propellor versus speed ??
« Reply #11 on: September 02, 2010, 03:40:04 PM »

Guys : As Peyton mentioned, Ebay has laser tachs for the $20 to the $50 range.   :clap
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Ron, Apache #788
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